MEMS device having electrothermal actuation and release and method for fabricating

ABSTRACT

MEMS Device having Electrothermal Actuation and Release and Method for Fabricating. According to one embodiment, a microscale switch is provided and can include a substrate and a stationary electrode and stationary contact formed on the substrate. The switch can further include a movable microcomponent suspended above the substrate. The microcomponent can include a structural layer including at least one end fixed with respect to the substrate. The microcomponent can further include a movable electrode spaced from the stationary electrode and a movable contact spaced from the stationary electrode. The microcomponent can include an electrothermal component attached to the structural layer and operable to produce heating for generating force for moving the structural layer.

CROSS-REFERENCE TO THE RELATED APPLICATIONS

This nonprovisional application claims the benefit of U.S. ProvisionalApplication No. 60/337,527, filed Nov. 9, 2001; U.S. ProvisionalApplication No. 60/337,528, filed Nov. 9, 2001; U.S. ProvisionalApplication No. 60/337,529, filed Nov. 9, 2001; U.S. ProvisionalApplication No. 60/338,055, filed Nov. 9, 2001; U.S. ProvisionalApplication No. 60/338,069, filed Nov. 9, 2001; U.S. ProvisionalApplication No. 60/338,072, filed Nov. 9, 2001, the disclosures of whichare incorporated by reference herein in their entireties. Additionally,the disclosures of the following U.S. patent applications, commonlyassigned and simultaneously filed herewith, are all incorporated byreference herein in their entireties: U.S. patent applications entitled“MEMS Device Having a Trilayered Beam and Related Methods”, U.S. patentapplication Ser. No. 10/290,779; “Trilayered Beam MEMS Device andRelated Methods”, U.S. patent application Ser. No. 10/290,920; “MEMSDevice Having Contact and Standoff Bumps and Related Methods”. U.S.patent application Ser. No. 10/291,107; and “ElectrothermalSelf-Latching MEMS Switch and Method”, U.S. patent application Ser. No.10/290,807.

TECHNICAL FIELD

The present invention generally relates to micro-electro-mechanicalsystems (MEMS) devices and methods. More particularly, the presentinvention relates to the design and fabrication of movable MEMSmicroscale structures.

BACKGROUND ART

An electrostatic MEMS switch is a switch operated by an electrostaticcharge and manufactured using MEMS techniques. A MEMS switch can controlelectrical, mechanical, or optical signal flow. MEMS switches havetypical application to telecommunications, such as DSL switch matricesand cell phones, Automated Testing Equipment (ATE), and other systemsthat require low cost switches or low-cost, high-density arrays.

As can be appreciated by persons skilled in the art, many types of MEMSswitches and related devices can be fabricated by either bulk or surfacemicromachining techniques. Bulk micromachining generally involvessculpting one or more sides of a substrate to form desiredthree-dimensional structures and devices in the same substrate material.The substrate is composed of a material that is readily available inbulk form, and thus ordinarily is silicon or glass. Wet and/or dryetching techniques are employed in association with etch masks and etchstops to form the microstructures. Etching is typically performedthrough the backside of the substrate. The etching technique cangenerally be either isotropic or anisotropic in nature. Isotropicetching is insensitive to the crystal orientation of the planes of thematerial being etched (e.g., the etching of silicon by using a nitricacid as the etchant). Anisotropic etchants, such as potassium hydroxide(KOH), tetramethyl ammonium hydroxide (TMAH), and ethylenediaminepyrochatechol (EDP), selectively attack different crystallographicorientations at different rates, and thus can be used to definerelatively accurate sidewalls in the etch pits being created. Etch masksand etch stops are used to prevent predetermined regions of thesubstrate from being etched.

On the other hand, surface micromachining generally involves formingthree-dimensional structures by depositing a number of different thinfilms on the top of a silicon wafer, but without sculpting the waferitself. The films usually serve as either structural or sacrificiallayers. Structural layers are frequently composed of polysilicon,silicon nitride, silicon dioxide, silicon carbide, or aluminum.Sacrificial layers are frequently composed of polysilicon, photoresistmaterial, polyimide, metals or various kinds of oxides, such as PSG(phosphosilicate glass) and LTO (low-temperature oxide). Successivedeposition, etching, and patterning procedures are carried out to arriveat the desired microstructure. In a typical surface micromachiningprocess, a silicon substrate is coated with an isolation layer, and asacrificial layer is deposited on the coated substrate. Windows areopened in the sacrificial layer, and a structural layer is thendeposited and etched. The sacrificial layer is then selectively etchedto form a free-standing, movable microstructure such as a beam or acantilever out of the structural layer. The microstructure, ormicrocomponent, is ordinarily anchored to the silicon substrate, and canbe designed to be movable in response to an input from an appropriateactuating mechanism.

Many current MEMS switch designs employ a cantilievered beam (or plate),or multiple-supported beam geometry for the switching structure. In thecase of cantilevered beams, these MEMS switches include a movable,bimaterial beam comprising a structural layer of dielectric material anda layer of metal. Typically, the dielectric material is fixed at one endwith respect to the substrate and provides structural support for thebeam. The layer of metal is attached on the underside of the dielectricmaterial and forms a movable electrode and a movable contact. The layerof metal can form part of the anchor. The movable beam is actuated in adirection toward the substrate by the application of a voltagedifference across the electrode and another electrode attached to thesurface of the substrate. The application of the voltage difference tothe two electrodes creates an electrostatic field, which pulls the beamtowards the substrate. The beam and substrate each have a contact whichis separated by an air gap when no voltage is applied, wherein theswitch is in the “open” position. When the voltage difference isapplied, the beam is pulled to the substrate and the contacts make anelectrical connection, wherein the switch is in the “closed” position.

One of the problems that faces current MEMS switches having a bimaterialbeam is curling or other forms of static displacement or deformation ofthe beam. The static deformation can be caused by a stress mismatch or astress gradient within the films. At some equilibrium temperature, themismatch effects could be balanced to achieve a flat bimaterialstructure, but this does not fix the temperature dependent effects. Themismatch could be balanced through specific processes (i.e., depositionrates, pressures, method, etc.), through material selection, and throughgeometrical parameters such as thickness. This bimaterial structure ofmetal and dielectric introduces a large variation in function overtemperature, because the metal will typically have a higher thermalexpansion rate than the dielectric. Because of the different states ofstatic stress in the two materials, the switch can be deformed with ahigh degree of variability. Switch failure can result from deformationof the beam. Switch failure results when electrical contact is notestablished between the movable and stationary contacts due to staticdeformation or because of the deformation introduced as a function oftemperature. A second mode of failure is observed when the movablecontact and the stationary contact are prematurely closed, resulting ina “short”. Because of the deformation of the beam, the actuation voltageis increased or decreased depending on whether it is curved away fromthe substrate or towards the substrate, respectively. Because of thisvariability, the available voltage may not be adequate to achieve thedesired contact force and, thus, contact resistance.

Many MEMS switches are designed with stiffer beams in order to avoidcurling or deformation for improving switch reliability. These MEMSswitches require higher actuation voltage in order to deflect the beamto a “closed” position. It is desirable to reduce the actuation voltagerequired to close MEMS switches for power conservation. A higher voltageis required to deflect the beam to a “closed” position than to maintainthe beam in a “closed” position. Thus, in order to minimize the powerrequired for operating the switch, it is desirable to use minimal powerto reduce the power for actuating the beam and maintaining the beam inthe “closed” position.

Typically, the beam of a MEMS switch is restored to an “open” positionfrom a “closed” position by reducing the actuation voltage an amountsufficient for the resilient forces of the beam to deflect the beam backto the “open” position. The contacts of a MEMS switch frequently adhereto one another due metallurgical adhesion, cold welding, or hot weldingforces. These forces are sometimes greater than the resilient forces ofthe beam, thus preventing the deflection of the beam to the “open”position. In such cases, switch failure results because the beam doesnot return to the “open” position. Therefore, it is desired to have aMEMS switch having a mechanism for generating a force to return the beamto an “open” position.

DISCLOSURE OF THE INVENTION

According to one embodiment, a movable microcomponent suspended over asubstrate is provided. The movable microcomponent can include adielectric layer having at least one end fixed with respect to thesubstrate. The microcomponent can also include a movable electrodeattached to the dielectric layer and separated from the substrate.Furthermore, the microcomponent can include an electrothermal componentattached to the dielectric layer and operable to produce heat fordeflecting the dielectric layer.

According to a second embodiment, a microscale switch for electrostaticand electrothermal actuation is provided. The switch can include asubstrate and a stationary electrode and stationary contact formed onthe substrate. The switch can also include a movable microcomponentsuspended above the substrate. The microcomponent can include adielectric layer including at least one end fixed with respect to thesubstrate. The microcomponent can also include a movable electrodespaced from the stationary electrode and a movable contact spaced fromthe stationary electrode. Furthermore, the microcomponent can include anelectrothermal component attached to the dielectric layer and operableto produce heating for generating force for moving the dielectric layer.

According to a third embodiment, a method for implementing a switchingfunction in a microscale device is provided. The method can includeproviding a stationary electrode and a stationary contact formed on asubstrate. The method can further include providing a movablemicrocomponent suspended above the substrate. The microcomponent caninclude a dielectric layer including at least one end fixed with respectto the substrate. The microcomponent can also include a movableelectrode spaced from the stationary electrode and a movable contactspaced from the stationary electrode. The movable contact can bepositioned farther from the at least one end than the movable electrode.The microcomponent can include an electrothermal component attached tothe dielectric layer. The method can include applying a voltage betweenthe movable electrode and the stationary electrode to electrostaticallycouple the movable electrode with the stationary electrode, whereby themovable component is deflected toward the substrate and the movablecontact moves into contact with the stationary contact to permit anelectrical signal to pass through the movable and stationary contacts.Furthermore, the method can include applying a current through the firstelectrothermal component to produce heating for generating force formoving the microcomponent.

According to a fourth embodiment, a method for fabricating a microscaleswitch is provided. The method can include depositing a first conductivelayer on a substrate and forming a stationary electrode and a stationarycontact by removing a portion of the first conductive layer. The methodcan also include depositing a sacrificial layer on the stationaryelectrode, the stationary contact, and the substrate. Additionally, themethod can include depositing a second conductive layer on thesacrificial layer and forming a movable electrode and a movable contactby removing a portion of the second conductive layer. The method canalso include depositing a third conductive layer on the dielectric layerand removing a portion of the third conductive layer to form anelectrothermal component. Furthermore, the method can include removing asufficient amount of the sacrificial layer so as to define a first gapbetween the stationary electrode and the movable electrode, and todefine a second gap between the stationary contact and the movablecontact.

According to a fifth embodiment, a method for fabricating a microscaleswitch is provided. The method can include depositing a first conductivelayer on a substrate and forming a stationary electrode and a stationarycontact by removing a portion of the first conductive layer. The methodcan further include depositing a sacrificial layer on the stationaryelectrode, the stationary contact, and the substrate. Additionally, themethod can include depositing a second conductive layer on thesacrificial layer and forming a movable electrode, a movable contact,and an electrothermal component by removing a portion of the secondconductive layer. Furthermore, the method can include removing asufficient amount of the sacrificial layer so as to define a first gapbetween the stationary electrode and the movable electrode, and todefine a second gap between the stationary contact and the movablecontact.

According to a sixth embodiment, a method for implementing a switchingfunction in a microscale device having a movable microcomponent isprovided. The method can include applying a voltage between a movableelectrode and a stationary electrode of the microscale device forelectrostatically coupling the movable electrode with the stationaryelectrode, whereby the movable microcomponent is deflected and a movablecontact moves into contact with a stationary contact to permit anelectrical signal to pass through the movable and stationary contacts.The method can also includes applying a current through a firstelectrothermal component of the microscale device to produce heating forgenerating force for moving the microcomponent.

Accordingly, it is an object of the present invention to provide amovable microcomponent for improving the yield, performance overtemperature, actuation, and quality of MEMS switches.

An object having been stated hereinabove, and which is achieved in wholeor in part by the described MEMS device having electrothermal actuationand release and method for fabricating described herein, other objectswill become evident as the description proceeds when taken in connectionwith the accompanying drawings as best described hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be explained withreference to the accompanying drawings, of which:

FIG. 1 illustrates a cross-sectional side view of a MEMS switch havingelectrothermal actuation and release in an “open” position;

FIG. 2 illustrates a top plan view of a MEMS switch havingelectrothermal actuation and release;

FIG. 3 illustrates a bottom plan view of a beam of a MEMS switch havingelectrothermal actuation and release;

FIG. 4 illustrates a cross-sectional side view of a MEMS switch havingelectrothermal actuation and release in a “closed” position;

FIG. 5 illustrates a cross-sectional front elevation view of thestationary electrode, structural layer, movable electrode, electrodeinterconnect, release electrothermal component, and actuationelectrothermal component of a MEMS switch having electrothermalactuation and release; and

FIGS. 6A-K illustrate fabrication steps of an embodiment of a method forfabricating a MEMS switch having electrothermal actuation and release.

DETAILED DESCRIPTION OF THE INVENTION

For purpose of the description herein, it is understood that when acomponent such as a layer or substrate is referred to as being “disposedon”, “attached to” or “formed on” another component, that component canbe directly on the other component or, alternatively, interveningcomponents (for example, one or more buffer or transition layers,interlayers, electrodes or contacts) can also be present. Furthermore,it is understood that the terms “disposed on”, “attached to” and “formedon” are used interchangeably to describe how a given component can bepositioned or situated in relation to another component. Therefore, itwill be understood that the terms “disposed on”, “attached to” and“formed on” do not introduce any limitations relating to particularmethods of material transport, deposition, or fabrication.

Contacts, interconnects, conductive vias, electrothermal components andelectrodes of various metals can be formed by sputtering, CVD, orevaporation. If gold, nickel or PERMALLOY™ (Ni_(x)Fe_(y)) is employed asthe metal element, an electroplating process can be carried out totransport the material to a desired surface. The chemical solutions usedin the electroplating of various metals are generally known. Somemetals, such as gold, might require an appropriate intermediate adhesionlayer to prevent peeling. Examples of adhesion material often usedinclude chromium, titanium, or an alloy such as titanium-tungsten (TiW).Some metal combinations can require a diffusion barrier to prevent achromium adhesion layer from diffusing through gold. Examples ofdiffusion barriers between gold and chromium include platinum or nickel.

Conventional lithographic techniques can be employed in accordance withfabrication, such as micromachining, of the invention described herein.Accordingly, basic lithographic process steps such as photoresistapplication, optical exposure, and the use of developers are notdescribed in detail herein.

Similarly, generally known etching processes can be suitably employed toselectively remove material or regions of material. An imagedphotoresist layer is ordinarily used as a masking template. A patterncan be etched directly into the bulk of a substrate, or into a thin filmor layer that is then used as a mask for subsequent etching steps.

The type of etching process employed in a particular fabrication step(e.g., wet, dry, isotropic, anisotropic, anisotropic-orientationdependent), the etch rate, and the type of etchant used will depend onthe composition of material to be removed, the composition of anymasking or etch-stop layer to be used, and the profile of the etchedregion to be formed. As examples, poly-etch (HF:HNO₃:CH₃COOH) cangenerally be used for isotropic wet etching. Hydroxides of alkali metals(e.g., KOH), simple ammonium hydroxide (NH₄OH), quaternary (tetramethyl)ammonium hydroxide ((CH₃)₄NOH, also known commercially as TMAH), andethylenediamine mixed with pyrochatechol in water (EDP) can be used foranisotropic wet etching to fabricate V-shaped or tapered grooves,trenches or cavities. Silicon nitride can typically be used as themasking material against etching by KOH, and thus can used inconjunction with the selective etching of silicon. Silicon dioxide isslowly etched by KOH, and thus can be used as a masking layer if theetch time is short. While KOH will etch undoped silicon, heavily doped(p++) silicon can be used as an etch-stop against KOH as well as theother alkaline etchants and EDP. Silicon oxide and silicon nitride canbe used as masks against TMAH and EDP. The preferred metal used to formcontacts and interconnects in accordance with the invention is gold andits alloys.

It will be appreciated that electrochemical etching in hydroxidesolution can be performed instead of timed wet etching. For example, ifa p-type silicon wafer is used as a substrate, an etch-stop can becreated by epitaxially growing an n-type silicon end layer to form a p-njunction diode. A voltage can be applied between the n-type layer and anelectrode disposed in the solution to reverse-bias the p-n junction. Asa result, the bulk p-type silicon is etched through a mask down to thep-n junction, stopping at the n-type layer. Furthermore, photovoltaicand galvanic etch-stop techniques are also suitable.

Dry etching techniques such as plasma-phase etching and reactive ionetching (RIE) can also be used to remove silicon and its oxides andnitrides, as well as various metals. Deep reactive ion etching (DRIE)can be used to anisotropically etch deep, vertical trenches in bulklayers. Silicon dioxide is typically used as an etch-stop against DRIE,and thus structures containing a buried silicon dioxide layer, such assilicon-on-insulator (SOI) wafers, can be used according to the methodsof the invention as starting substrates for the fabrication ofmicrostructures.

An alternative patterning process to etching is the lift-off process asknown to those of skill in the art. In this case, the conventionalphotolithography techniques are used for the negative image of thedesired pattern. This process is typically used to pattern metals, whichare deposited as a continuous film or films when adhesion layers anddiffusion barriers are needed. The metal is deposited on the regionswhere it is to be patterned and on top of the photoresist mask (negativeimage). The photoresist and metal on top are removed to leave behind thedesired pattern of metal.

As used herein, the term “device” is interpreted to have a meaninginterchangeable with the term “component.” As used herein, the term“conductive” is generally taken to encompass both conducting andsemi-conducting materials.

Examples will now be described with reference to the accompanyingdrawings.

Referring to FIGS. 1-5, different views of a MEMS switch, generallydesignated 100, having electrothermal enhanced actuation and release areillustrated. Referring specifically to FIG. 1, a cross-sectional sideview of MEMS switch, generally designated 100, is illustrated in an“open” position. MEMS switch 100 includes a substrate 102. Non-limitingexamples of materials which substrate 102 can comprise silicon (insingle-crystal, polycrystalline, or amorphous forms), siliconoxinitride, glass, quartz, sapphire, zinc oxide, alumina, silica, or oneof the various Group III-V compounds in either binary, ternary orquaternary forms (e.g., GaAs, InP, GaN, AlN, AlGaN, InGaAs, and so on).If the composition of substrate 102 is chosen to be a conductive orsemi-conductive material, a non-conductive, dielectric layer can bedeposited on the top surface of substrate 102, or at least on portionsof the top surface where electrical contacts or conductive regions aredesired.

Substrate 102 includes a first stationary contact 104, a secondstationary contact (not shown in this view due to its positioning behindfirst stationary contact 104), and a stationary electrode 106 formed ona surface thereof. First stationary contact 104, the second stationarycontact, and stationary electrode 106 can comprise a conductive materialsuch as a metal. Specifically, first stationary contact 104, the secondstationary contact, and stationary electrode 106 can comprise differentconductive materials such as gold-nickel alloy (AuNi₅) and aluminum orother suitable conductive materials known to those of skill in the art.The conductivity of stationary electrode 106 can be much lower than theconductivity of first stationary contact 104 and the second stationarycontact. Preferably, first stationary contact 104 and the secondstationary contact can comprise a very high conductive material such ascopper. Preferably, first stationary contact 104 and the secondstationary contact can have a width range of 7 μm to 100 μm and a lengthrange of 15 μm to 75 μm. Stationary electrode 106 can have a wide rangeof dimensions depending on the required actuation voltages, contactresistance, and other functional parameters.

MEMS switch 100 further comprises a movable, trilayered beam, generallydesignated 108, suspended over first stationary contact 104, the secondstationary contact, and stationary electrode 106. Beam 108 is fixedlyattached at one end to a mount 110, which can be fixedly attached tosubstrate 102. Beam 108 extends substantially parallel to the topsurface of substrate 102 when MEMS switch 100 is in an “open” position.Beam 108 generally comprises a dielectric structural layer 112 disposedbetween two electrically conductive layers described in more detailbelow. Structural layer 112 can comprise a bendable material, preferablysilicon oxide (SiO₂, as it is sputtered, electroplated, spun-on, orotherwise deposited), to deflect towards substrate 102 for operating ina “closed” position. Structural layer 112 provides electrical isolationand desirable mechanical properties including resiliency properties.Alternatively, structural layer 112 can comprise silicon nitride(Si_(x)N_(y)), silicon oxynitride, alumina or aluminum oxide(Al_(x)O_(y)), polymers, CVD diamond, their alloys, or any othersuitable resilient materials known to those of skill in the art. Beam108 is designed to be resilient for generating a restorative force toreturn the beam to its natural position when beam 108 is deflected orbent.

In this embodiment, beam 108 further includes a top and bottom layerattached to a top side 114 and an underside 116, respectively, thereof.The bottom layer comprises a movable electrode 118, a releaseelectrothermal component 120, and a movable contact 122. Movableelectrode 118 is shown with broken lines in this view due to itsposition behind release electrothermal component 120. The top layercomprises an electrode interconnect 124, an actuation electrothermalcomponent 126, and a contact interconnect 128. Electrode interconnect124 is shown with broken lines in this view due to its position behindactuation electrothermal component 126. As shown, movable contact 118and contact interconnect 128 are positioned further away from mount 110than movable electrode 118 and electrode interconnect 124. Releaseelectrothermal component 120 and actuation electrothermal component 126extend substantially the length of beam 108. Alternatively, releaseelectrothermal component 120 and actuation electrothermal component 126can extend from mount 110 to any other suitable location on beam 108.

Movable electrode 118 is positioned over stationary electrode 106 anddisplaced from stationary electrode 106 such that application of avoltage difference across electrodes 106 and 118 creates anelectrostatic field, which causes an attractive force between electrodes106 and 118. Upon application of the voltage difference acrosselectrodes 106 and 118, beam 108 bends in a direction towards substrate102. In this embodiment, actuation electrothermal component 126 is aclosed electrical circuit including current paths and resistance pathtransitions, shown and described in more detail below. Alternatively,the resistance path transition can be realized by a change in thicknessinstead of the change in width that is portrayed. Alternatively,electrothermal components 120 and 126 can comprise material transitionsrather than area transitions to accomplish the resistance pathtransitions. The material transitions are realized by patterningdifferent materials on either side of the resistance path transition.For example, nickel (Ni) and gold (Au) can be patterned on the first andsecond side of the resistance path transition. Any suitable materialshaving differing thermal and mechanical properties known to those ofskill in the art can be used to achieve resistance path transitions. Themagnitude of the localized heating is determined by the difference inthe geometric or material properties. The resistance path transitionsprovide local heating and local generation of force at a suitablelocation on the top side 114 of structural layer 112 for facilitatingdeflection of beam 108 towards substrate 102. The combination ofelectrostatic and electrothermal forces deflect beam 108 towardssubstrate 102. The operation of the actuation electrothermal component126 and electrodes 106 and 118 is described in further detail below.

The applied voltage difference between electrodes 106 and 118 can bereduced with the addition of the force generated by electrothermalactuation of electrothermal component 126. This voltage reduction isdesirable for achieving switching voltages on the order of 5 volts.Further, with the addition of electrothermal actuation, structural layer112 can be designed stiffer and still actuate at a lower appliedvoltage. The increased beam stiffness tends to lower the switching speedand increase the reliability of achieving release from a “closed”position.

Electrodes 106 and 118, contacts 104 and 122, release electrothermalcomponent 120, actuation electrothermal component 126, and interconnects124 and 128 can comprise similar materials, such as gold, whereby themanufacturing process is simplified by the minimization of the number ofdifferent materials required for fabrication. Additionally, electrodes106 and 118, contacts 104 and 122, release electrothermal component 120,actuation electrothermal component 126, and interconnects 124 and 128can comprise conductors (platinum, aluminum, palladium, copper,tungsten, nickel, and other materials known to those of skill in theart), conductive oxides (indium tin oxide), and low resistivitysemiconductors (silicon, polysilicon, and other materials known to thoseof skill in the art). These components can include adhesion layers (Cr,Ti, TiW, etc.) disposed between the component and structural layer 112.These components can comprise a conductive material and an adhesionlayer that includes diffusion barriers for preventing diffusion of theadhesion layer through the electrode material, or diffusion through theconductive material into the structural material. These components canalso comprise different materials for breakdown or arcingconsiderations, for “stiction” considerations during wet chemicalprocessing, or because of fabrications process compatibility issues.Contacts 104 and 122 can comprise a material having good conductiveproperties and other desirable properties of suitable contacts known tothose of skill in the art, such as low hardness and low wear.Preferably, electrodes 106 and 118 comprise a material having lowresistivity, low hardness, low oxidation, low wear, and other desirableproperties of suitable contacts known to those of skill in the art.Preferably, electrothermal components 120 and 126 comprise a materialhaving high resistivity, high softening/melting point, and high currentcapacity. The preferred properties contribute to high localized heatingfor development of larger deflections and forces. The highsoftening/melting point and high current capacity increase thereliability of the device during electrothermal operation. In thisembodiment, electrothermal components 120 and 126 comprise the samematerial. Alternatively, electrothermal components 120 and 126 cancomprise different materials.

Movable contact 122 is positioned over first stationary contact 104 andthe second stationary contact such that it contacts first stationarycontact 104 and the second stationary contact when beam 108 is moved tothe “closed” position, thus providing electrical communication betweenfirst stationary contact 104 and the second stationary contact throughmovable contact 122. Movable contact 122 is displaced from firststationary contact 104 and the second stationary contact when MEMSswitch 100 operates in the “open” position such that there is noelectrical communication between first stationary contact 104 and thesecond stationary contact. Movable contact 122 can be dimensionedsmaller than first stationary contact 104 and the second stationarycontact to facilitate contact when process variability and alignmentvariability are taken into consideration. First stationary contact 104and the second stationary contact need to be sized appropriately so thatmovable contact 122 always makes contact with first stationary contact104 and the second stationary contact when in the “closed” position. Asecond consideration that determines the size of movable contact 122,first stationary contact 104, and the second stationary contact is theparasitic response of switch 100. The parasitic actuation response isgenerated by electric fields produced by potential differences betweenmovable electrodes 106 and 118, or by charge (or potential) differencesbetween first stationary electrode 106 and second stationary contact andbeam 108 that produce electric fields and a force on movable contact122. The dimensions of movable contact 122 are related to the dimensionsof movable electrode 118 to achieve a specific ratio of the parasiticactuation to the actuation voltage.

Electrode interconnect 124 and movable electrode 118 are attached toopposing sides of structural layer 112. Preferably, movable electrode118 and electrode interconnect 124 have substantially the samedimensions and are aligned with one another for achieving amanufacturable flatness that is maintained over temperature. In thisembodiment, electrode interconnect 124 comprises a conductive materialhaving the same coefficient of thermal expansion, elastic modulus,residual film stress, and other electrical/mechanical properties asmovable electrode 118.

Movable electrode 118 and electrode interconnect 124 are in electricalcommunication with one another by connection to a first interconnect via130. First interconnect via 130 is indicated by broken lines in thisview due to its placement inside structural layer 112. Firstinterconnect via 130 comprises a conductive material formed throughstructural layer 112. In this embodiment, first interconnect via 130comprises the same conductive material as movable electrode 118 andelectrode interconnect 124. Alternatively, first interconnect via 130can comprise any suitable conductive material known to those of skill inthe art, such as low wear and low hardness.

Movable contact 122 and contact interconnect 128 are attached to andaligned on opposing sides of structural layer 112. Contact interconnect128 is dimensioned substantially the same as movable contact 122.Alternatively, contact interconnect 128 can have different dimensionsand extent than movable contact 122. It is intended to maintaingeometric equivalence by management of the mechanical form. Contactinterconnect 128 and movable contact 122 are intended to share ageometrical and thermo-mechanical equivalence. This equivalence providesa beam, which can achieve a manufacturable flatness that is maintainedover temperature and other environmental conditions, such as dieattachment, package lid seal processes, or solder reflow process. Inthis embodiment, contact interconnect 128 comprises a conductivematerial, such as copper for example, having the same coefficient ofthermal expansion, elastic modulus, residual film stress, and otherdesirable electrical/mechanical properties known to those of skill inthe art as movable contact 122.

Movable contact 122 and contact interconnect 128 are in electricalcommunication with one another by connection to a second interconnectvia 132. Second interconnect via 132 is indicated by broken lines due toits placement inside structural layer 112. Second interconnect via 132comprises a conductive material, such as copper for example, formedthrough structural layer 112 for electrically connecting movable contact122 and contact interconnect 128. In this embodiment, secondinterconnect via 132 can comprise the same conductive material ascontact interconnect 128 and movable contact 122. Alternatively, secondinterconnect via 132 can comprise a different conductive material ascontact interconnect 128 and movable contact 122.

MEMS switch 100 further includes a switch controller 134 connected toand operable to transmit control signals to a first current source 136,a second current source 138, and a voltage source 140 for controllingthe electrostatic and electrothermal actuation of switch 100 byapplication of voltage and current. Switch controller 134 is alsooperable to transmit control signals to other switches in an array ofswitches. First current source 136, second current source 138, andvoltage source 140 are operable to output voltage and current inresponse to receiving control signals from switch controller 134.

Referring to FIG. 2, a top view of MEMS switch 100 is illustrated. Asshown, actuation electrothermal component 126 is connected at two ends200 and 202 to the output of first current source 136. In thisembodiment, actuation electrothermal component 126 extends from ends 200and 202 around electrode interconnect 124 for providing a conductivepath along the length of beam 108 for current applied by first currentsource 136. Alternatively, the conductive path can extend around bothelectrode interconnect 124 and contact interconnect 128. Actuationelectrothermal component 126 further includes resistance pathtransitions 204 and 206 at which the current paths change from a lowresistance path to a high resistance path for providing local heatingand local generation of force to aid actuation of beam 108. The locationof resistance path transitions 204 and 206 and the ratio of thetransition can be optimized for maximal force without damaging thecomponent due to electrical overstress. Resistive heating along thelength of the actuation electrothermal component 126 will also providethe elongation that aids the actuation of beam 108. Thermal isolation isprovided between actuation electrothermal component 126 and electrodeinterconnect 124 by an air gap, generally designated 142, between thecomponents and structural layer 112 which serves as an insulator.

As shown, electrode interconnect 124 and contact interconnect 128 aregenerally rectangular in shape. The external corners of electrodeinterconnect 124 and contact interconnect 128 can be rounded to containinternal reentrant corners for reducing the intensification in theelectric fields produced by the potential differences betweenconductors. In this embodiment, electrode interconnect 124 can bedimensioned the same as movable electrode 118. Alternatively, electrodeinterconnect 124 can be any suitable non-rectangular shape thatsubstantially matches the shape of movable electrode 118. The shape ofcontact interconnect 128 substantially matches the shape of movablecontact 122. Interconnect vias 130 and 132 are rectangular and shown bybroken lines due to their position behind electrode interconnect 124 andcontact interconnect 128, respectively. Alternatively, interconnect vias130 and 132 can be any geometry suitable for vias including circular,elliptical, or rectangular with rounded corners.

Referring to FIG. 3, a bottom view of beam 108 of MEMS switch 100 isillustrated. Release electrothermal component 120 is connected at twoends 300 and 302 to the output of second current source 138. In thisembodiment, release electrothermal component 120 extends from ends 300and 302 around movable contact 122 along the length of beam 108 forproviding a conductive path for current applied by second current source138. Alternatively, the conductive path can extend around movableelectrode 118 and movable contact 122. Release electrothermal component120 further includes resistance path transitions 304 and 306 at whichthe current paths change from a low resistance path to a high resistancepath for providing local heating and local generation of force to aidrelease of beam 108 from a “closed” position, as described below. Thelocation of resistance path transitions 304 and 306 and the ratio of thetransition can be optimized for maximal force without damaging thecomponent due to electrical overstress. Resistive heating along thelength of the release electrothermal component 120 will also provide theelongation that aids the release of beam 108 from the “open” position.Thermal isolation is provided between release electrothermal component120 and movable electrode 118 by air gap 142 between the components andstructural layer 112 which serves as an insulator.

Upon the application of sufficient voltage and current by voltage source140 and first current source 136, respectively, beam 108 moves towardsubstrate 102 in a stable manner until beam 108 is close enough tosubstrate 102 for “pull-in” voltage, or “snap-in” voltage, to occur.After “pull-in” voltage occurs, beam 108 moves towards substrate 102 inan unstable manner until movable contact 122 touches first stationarycontact 104 and the second stationary contact, thus establishing anelectrical connection between first stationary contact 104 and thesecond stationary contact. Referring to FIG. 4, a cross-sectional sideview of MEMS switch 100 in a “closed” position is illustrated. In the“closed” position, movable contact 122 is touching first stationarycontact 104 and the second stationary contact, thus establishing anelectrical connection between first stationary contact 104 and thesecond stationary contact. As described below, the components of MEMSswitch 100 can be dimensioned such that movable electrode 118 andstationary electrode 106 do not contact in the “closed” position, thuspreventing a short between components 106 and 118. MEMS switch 100 canbe maintained in position by applying only the potential voltagedifference between movable electrode 118 and stationary electrode 106.The application of current to actuation electrothermal component 126 isnot required to maintain MEMS switch 100 in the “closed” position, thusreducing the power required for operating actuation electrothermalcomponent 126. Switch controller 134 is operable to receive feedbacksignals indicating a “closed” condition and turn off first currentsource 136 in response to receiving the signal.

MEMS switch 100 is returned to an “open” position by sufficientlyreducing or removing the voltage difference applied across stationaryelectrode 106 and movable electrode 118. This in turn reduces theattractive force between stationary electrode 106 and movable electrode118 such that the resilient force of structural layer 112 restoresstructural layer 112 to an “open” position. If movable contact 118adheres to stationary contact 104, current can be briefly applied bysecond current source 138 to the release electrothermal component 120 to“break” the contact. After release from the contact, the resilient forceof structural layer 112 can restore beam 108 to an “open” position.Switch controller 134 is operable to control voltage source 140 forreducing or removing the applied voltage and activating second currentsource 136 to apply current to release electrothermal component 120 forrestoring beam 108 to the “open” position.

Referring again to FIG. 1, voltage source 140 can be directly connectedto stationary electrode 106 and electrode interconnect 124. Movableelectrode 118 is electrically connected to voltage source 140 throughfirst interconnect via 130 and electrode interconnect 124. Firstinterconnect via 130 provides an electrical connection between electrodeinterconnect 124 and movable electrode 118. Therefore, upon theapplication of a voltage by voltage source 140, a voltage difference iscreated between stationary electrode 106 and movable electrode 118. Thisestablishes electrostatic coupling between movable electrode 118 andstationary electrode 106 across air gap 142. Alternatively, the gapbetween movable electrode 118 and stationary electrode 106 can be anysuitable isolating fluid/gas as known to those of skill in the art, suchas for example SF₆, a high breakdown voltage and arc quenching gas.

Preferably, movable electrode 118 and electrode interconnect 124 arefabricated of the same material and dimensioned the same. Additionally,movable contact 122 and contact interconnect 128 are fabricated of thesame material and dimensioned the same. First, it provides mechanicalbalance on both sides of structural layer 112. The mechanical balance isprovided because of the elastic symmetry, because the films aredeposited in the same way to produce a symmetric stress field, andbecause the thermal expansion properties are symmetric. The elasticsymmetry is preserved by using the same material and by using the samedimensions. The symmetric stress field is produced by depositing thesame materials using the same process and thicknesses. The symmetricthermal expansion properties minimize any variation in the switchoperation with respect to temperature because the same material is oneither side of structural layer 112. This means that any functionalvariation exhibited by MEMS switch 100 depends primarily on the processvariation, which can be minimized by the appropriate optimization of thedesign in the process. Secondly, because movable contact 122 and contactinterconnect 128 are fabricated of the same material and dimensioned thesame, the current carrying capacity of contacts 122 and 128 is aided. Itis preferable that beam 108 has the same type of metal, deposited by thesame process, patterned in the same geometry, and deposited to the samethickness, but the use of different materials could be accommodated withthe appropriate design and characterization. To address the issues ofcontact adhesion, cold welding, or hot welding, first stationary contact104, the second stationary contact, and movable contact 122 could bedifferent materials or different alloys of the same materials. Thematerial selection can minimize contact resistance and failures such asstiction.

In the “open” position, movable contact 118 is separated from firststationary contact 104 and second stationary contact by a gap distance a144 as shown in FIG. 1. Movable electrode 118 is separated fromstationary electrode 106 by a gap distance b 146. In this embodiment,distance a 142 is less distance b 146. If distance a 144 is lessdistance b 146, the operation of MEMS switch 100 is more reliablebecause potential for shorting between stationary electrode 106 andmovable electrode 118 is reduced. The length of beam 108 is indicated bya distance c 148. The center of movable contact 122 is a distance d 150from mount 110 and a distance e 152 from the end of beam 108 that isdistal mount 110. The edge of electrode interconnect 124 distal mount110 is a distance f 154 from mount 110. The edge of electrodeinterconnect 124 near mount 110 is a distance g 156 from mount 110. Inthis embodiment, distance a 144 is nominally 1.5 microns; distance b 146is preferably 2 microns; distance c 148 is preferably 155 microns;distance d 148 is preferably 135 microns; distance e 152 is preferably20 microns; distance f 154 is preferably 105 microns; and distance g 156is 10 microns. The distances a 144, b 146, c 148, d 150, e 152, f 154,and g 156 provide desirable functional performance, but other dimensionscan be selected to optimize other functional characteristics,manufacturability, and reliability.

Referring to FIG. 5, a cross-sectional front view of stationaryelectrode 106, structural layer 112, movable electrode 118, actuationelectrothermal component 120, electrode interconnect 124, and releaseelectrothermal component 126 of MEMS switch 100 is illustrated. Thewidth of movable electrode 118 and electrode interconnect 124 isindicated by a distance a 500. Preferably, movable electrode 118 andelectrode interconnect 124 are equal in width. Alternatively, movableelectrode 118 and electrode interconnect 124 can have different widths.The width of stationary electrode 106 is indicated by distance b 502.The width of structural layer 112 is indicated by distance c 504. Thethickness of structural layer 112 is indicated by distance d 506. Thethickness of stationary electrode 106 is indicated by distance e 508.The thickness of movable electrode 118 and release electrothermalcomponent 120 is indicated by distance f 510. The thickness of electrodeinterconnect 124 and actuation electrothermal component 126 is indicatedby distance g 512. The conductive paths of release electrothermalcomponent 120 and actuation electrothermal component 126 are indicatedby distance h 514 and i 516. First stationary contact 104 and stationaryelectrode 106 can be dimensioned greater than movable electrode 118 andmovable contact 122, respectively, in order to facilitate shielding MEMSswitch 100 from any parasitic voltages. In this embodiment, distance a500 is preferably 75 microns; distance b 502 is preferably 125 microns;distance c 504 is preferably 105 microns; distance d 506 is preferably 2microns; distance e 508 is preferably 0.5 microns; distance f 510 ispreferably 0.5 microns; distance g 512 is preferably 0.5 microns; anddistances h 514 and i 516 are preferably microns. The distances a 500, b502, c 504, d 506, e 508, f 510, g 512, h 514 and i 516 providedesirable functional performance, but other dimensions can be selectedto optimize other functional characteristics, manufacturability, andreliability.

Referring to FIGS. 6A-6K, an embodiment of a method for fabricating aMEMS switch having electrothermal actuation and release according to asurface micromachining process of the present invention will now bedescribed. Referring specifically to FIG. 6A, a substrate 600 isprovided, which preferably comprises silicon. Because substrate 600 is asemi-conductive material, a first dielectric layer 602 is deposited onthe top surface of substrate 600. Alternatively, dielectric material canbe deposited on portions of the top surface where electrical contacts orconductive regions are desired.

Referring to FIGS. 6B-6C, a process for producing a first stationarycontact 604, a second stationary contact (not shown due to itspositioning behind first stationary contact 604), and a stationaryelectrode 606 is illustrated. Referring specifically to FIG. 6B, a firstconductive layer 608 is deposited on first dielectric layer 602. Firstconductive layer 608 is patterned as described above. Referring to FIG.6C, first stationary contact 604, the second stationary contact, andstationary electrode 606 are formed simultaneously in first conductivelayer 608. Alternatively, first stationary contact 604, the secondstationary contact, and stationary electrode 606 can be formed inseparate processes.

Referring to FIG. 6D, a sacrificial layer 610 is deposited to a uniformthickness such that its top surface is preferably planarized.Sacrificial layer 610 defines the gap between a beam structure,described in further detail below, and first stationary contact 604, thesecond stationary contact, and stationary electrode 606. Sacrificiallayer 610 can be a metal, dielectric or any other suitable materialknown to those of skill in the art such that the removal chemistry iscompatible with the other electrical and structural materials.

Referring to FIGS. 6E-6F, a process for producing a movable contact 612,a movable electrode 614, and a release electrothermal component 616, asdescribed above, is illustrated. Referring specifically to FIG. 6E,grooves 618, 620, and 622 are etched in sacrificial layer 610 forforming movable contact 612, movable electrode 614, and releaseelectrothermal component 616, respectively. Groove 624 is formed insacrificial layer 610 for forming a structure to attach the beam tosubstrate 600 and suspend the beam above first stationary contact 604,the second stationary contact, and stationary electrode 606. Referringnow to FIG. 6F, a conductive layer is deposited on sacrificial layer 610until grooves 618, 620, and 622 are filled. Next, the conductive layeris patterned as described above to form movable contact 612, movableelectrode 614, and release electrothermal component 616.

Referring FIG. 6G, a structural layer 626 is deposited on movablecontact 612, movable electrode 614, release electrothermal component616, sacrificial layer 610, and first dielectric layer 602. Structurallayer 626 comprises oxide in this embodiment.

Referring to 6H-6J, a process for simultaneously producing the followingconductive microstructures: a contact interconnect 628, an electrodeinterconnect 630, an actuation electrothermal component 632, andinterconnect vias 634 and 636. Referring specifically to FIG. 6H,recesses 638 and 640 are etched into structural layer 626 for forminginterconnect vias 634 and 636, respectively. Recesses 638 and 640 areetched through structural layer 626 to movable contact 612 and movableelectrode 614, respectively.

Referring now to FIG. 6I, a second conductive layer 642 is deposited onstructural layer 626 and into recesses 638 and 640 as shown for formingan electrical connection from movable contact 612 and movable electrode614 to the top surface of structural layer 626. Next, second conductivelayer 642 is patterned for forming contact interconnect 628, electrodeinterconnect 630, and actuation electrothermal component 632 as shown inFIG. 6J. Interconnect vias 634 and 636 can be formed by anotherconductive layer that would precede the deposition of second conductivelayer 642 described above.

Referring to FIG. 6K, the final step in fabricating the MEMS switch isillustrated. In this step, sacrificial layer 610 is removed to form atrilayered beam, generally designated 644. Sacrificial layer 610 can beremoved by any suitable method known to those of skill in the art.

It may be desired to have a MEMS switch that takes advantage of eitherthe enhanced actuation or enhanced release. In that case, an alternateMEMS switch having either one of an actuation electrothermal componentor a release electrothermal component can be fabricated and operatedwithout the other component.

It will be understood that various details of the invention may bechanged without departing from the scope of the invention. Furthermore,the foregoing description is for the purpose of illustration only, andnot for the purpose of limitation—the invention being defined by theclaims.

1. A microscale switch for electrostatic and electrothermal actuation,the switch comprising: (a) a substrate; (b) a stationary electrodeformed on the substrate; (c) a stationary contact formed on thesubstrate; (d) a voltage source; (e) a first current source; and (f) amovable microcomponent suspended above the substrate, comprising: (i) astructural layer including at least one end fixed with respect to thesubstrate; (ii) a movable electrode positioned directly above thestationary electrode, spaced from the stationary electrode by a gap suchthat it does not contact the stationary electrode, and connected to thevoltage source, wherein the movable electrode is movable with respect tothe stationary electrode when the voltage source applies a voltagedifference between the stationary electrode and the movable electrode toestablish electrostatic coupling between the movable electrode and thestationary electrode across the gap; (iii) a movable contact spaced fromthe stationary contact; and (iv) a first electrothermal component beingisolated from the movable electrode and the stationary electrode,attached to the structural layer along a majority of a length of thestructural layer, connected to the first current source, and operable toproduce heating when energized by the first current source forgenerating force for moving the structural layer.
 2. The switchaccording to claim 1, wherein the microcomponent has a length definedgenerally between the at least one end of the structural layer and adistal end of the movable electrode, and having a width that issubstantially constant along the length.
 3. The switch according toclaim 1, wherein the structural layer comprises a nonconductive,resilient material.
 4. The switch according to claim 1, wherein themovable electrode substantially covers an underside of the structurallayer.
 5. The switch according to claim 1, further including anelectrode interconnect attached to a top surface of the structural layeropposite from the movable electrode and having electrical communicationwith the movable electrode.
 6. The switch of claim 5, wherein themovable electrode and electrode interconnect have substantially equalrespective coefficients of thermal expansion.
 7. The switch according toclaim 1, wherein the first electrothermal component has first and secondterminal ends communicating with the first current source.
 8. The switchaccording to claim 1, wherein the first electrothermal component isattached to a top side of the structural layer for producing heat on thetop side of the structural layer to deflect the structural layer towardsthe substrate.
 9. The switch according to claim 1, wherein the firstelectrothermal component is attached to an underside of the structurallayer for producing heat on the underside of the structural layer todeflect the structural layer away from the substrate.
 10. The switchaccording to claim 1, including a second current source and a secondelectrothermal component connected to the second current source andattached to an underside of the structural layer for producing heat onthe underside of the structural layer when energized by the secondcurrent source to deflect the structural layer away from the substrate,and wherein the first electrothermal component is attached to a top sideof the structural layer for producing heat on the top side of thestructural layer when energized by the first current source to deflectthe structural layer towards the substrate.
 11. The switch according toclaim 1, wherein the first electrothermal component extendssubstantially the length of the structural layer.
 12. The switchaccording to claim 1, wherein the first electrothermal componentincludes at least one resistance path transition effecting an abruptchange in electrical resistance for generating heat at the location ofthe resistance path transition.
 13. The switch according to claim 1,wherein the first electrothermal component includes at least oneresistance path transition positioned adjacent the at least one fixedend and effecting an abrupt change in electrical resistance forgenerating heat adjacent the at least one fixed end.
 14. Amicroelectromechanical device comprising an array of switches structuredaccording to claim
 1. 15. A microscale switch for electrostatic andelectrothermal actuation, the switch comprising: (a) a substrate; (b) astationary electrode formed on the substrate; (c) a stationary contactformed on the substrate; (d) a voltage source; (e) a first currentsource; and (f) a movable microcomponent suspended above the substrate,comprising: (i) a structural layer including at least one end fixed withrespect to the substrate; (ii) a movable electrode positioned directlyabove the stationary electrode, spaced from the stationary electrode bya gap such that it does not contact the stationary electrode, andconnected to the voltage source, wherein the movable electrodesubstantially covers an underside of the structural layer; and whereinthe movable electrode is movable with respect to the stationaryelectrode when the voltage source applies a voltage difference betweenthe stationary electrode and the movable electrode to establishelectrostatic coupling between the movable electrode and the stationaryelectrode across the gap; (iii) a movable contact spaced from thestationary contact; and (iv) a first electrothermal component attachedto the structural layer and connected to the first current source, thefirst electrothermal component being operable to produce heating whenenergized by the first current source for generating force for movingthe structural layer.
 16. A microscale switch for electrostatic andelectrothermal actuation, the switch comprising: (a) a substrate; (b) astationary electrode formed on the substrate; (c) a stationary contactformed on the substrate; (d) a voltage source; (e) a first currentsource; and (f) a movable microcomponent suspended above the substrate,comprising: (i) a structural layer including at least one end fixed withrespect to the substrate; (ii) a movable electrode positioned directlyabove the stationary electrode, spaced from the stationary electrode bya gap such that it does not contact the stationary electrode, andconnected to the voltage source, the movable electrode being movablewith respect to the stationary electrode when the voltage source appliesa voltage difference between the stationary electrode and the movableelectrode to establish electrostatic coupling between the movableelectrode and the stationary electrode across the gap; (iii) a movablecontact spaced from the stationary contact; (iv) a first electrothermalcomponent attached to the structural layer and connected to the firstcurrent source, the first electrothermal component being operable toproduce heating when energized by the first current source forgenerating force for moving the structural layer; and (v) an electrodeinterconnect attached to a top surface of the structural layer oppositefrom the movable electrode and having electrical communication with themovable electrode, wherein the movable electrode and electrodeinterconnect have substantially equal respective coefficients of thermalexpansion.
 17. A microscale switch for electrostatic and electrothermalactuation, the switch comprising: (a) a substrate; (b) a stationaryelectrode formed on the substrate; (c) a stationary contact formed onthe substrate; (d) a voltage source; (e) a first current source; and (f)a movable microcomponent suspended above the substrate, comprising: (i)a structural layer including at least one end fixed with respect to thesubstrate and the stationary electrode; (ii) a movable electrodepositioned directly above the stationary electrode, spaced from thestationary electrode by a gap such that it does not contact thestationary electrode, and connected to the voltage source, the movableelectrode being movable with respect to the stationary electrode whenthe voltage source applies a voltage difference between the stationaryelectrode and the movable electrode to establish electrostatic couplingbetween the movable electrode and the stationary electrode across thegap; (iii) a movable contact spaced from the stationary contact and alsospaced from the stationary electrode, wherein the movable electrode ismovable when the voltage difference is applied between the stationaryelectrode and the movable electrode; and (iv) a first electrothermalcomponent being isolated from the movable and stationary electrodes,attached to the structural layer, connected to the first current source,and operable to produce heating when energized by the first currentsource for generating force for moving the structural layer, wherein thefirst electrothermal component is attached to a top side of thestructural layer for producing heat on the top side of the structurallayer to deflect the structural layer towards the substrate.
 18. Amicroscale switch for electrostatic and electrothermal actuation, theswitch comprising: (a) a substrate; (b) a stationary electrode formed onthe substrate; (c) a stationary contact formed on the substrate; (d) avoltage source; (e) a first current source; (f) a second current source;and (g) a movable microcomponent suspended above the substrate,comprising: (i) a structural layer including at least one end fixed withrespect to the substrate; (ii) a movable electrode positioned directlyabove the stationary electrode, spaced from the stationary electrode bya gap such that it does not contact the stationary electrode andconnected to the voltage source, the movable electrode being movablewith respect to the stationary electrode when the voltage source appliesa voltage difference between the stationary electrode and the movableelectrode to establish electrostatic coupling between the movableelectrode and the stationary electrode across the gap; (iii) a movablecontact spaced from the stationary contact; (iv) a first electrothermalcomponent attached to the structural layer and connected to the firstcurrent source, the first electrothermal component being operable toproduce heating when energized by the first current source forgenerating force for moving the structural layer; and (v) a secondelectrothermal component attached to an underside of the structurallayer and connected to the second current source, the secondelectrothermal component being operable for producing heat whenenergized by the second current source on the underside of thestructural layer to deflect the structural layer away from thesubstrate, wherein the first electrothermal component is attached to atop side of the structural layer for producing heat on the top side ofthe structural layer to deflect the structural layer towards thesubstrate.
 19. A microscale switch for electrostatic and electrothermalactuation, the switch comprising: (a) a substrate; (b) a stationaryelectrode formed on the substrate; (c) a stationary contact formed onthe substrate; (d) a voltage source; (e) a first current source; and (f)a movable microcomponent suspended above the substrate, comprising: (i)a structural layer including at least one end fixed with respect to thesubstrate; (ii) a movable electrode positioned directly above thestationary electrode, spaced from the stationary electrode by a gap suchthat it does not contact the stationary electrode and connected to thevoltage source, the movable electrode being movable with respect to thestationary electrode when the voltage source applies a voltagedifference between the stationary electrode and the movable electrode toestablish electrostatic coupling between the movable electrode and thestationary electrode across the gap; (iii) a movable contact spaced fromthe stationary contact; and (iv) a first electrothermal componentattached to the structural layer along a majority of a length of thestructural layer and connected to the first current source, the firstelectrothermal component being operable to produce heating whenenergized by the first current source for generating force for movingthe structural layer, wherein the movable component substantially coversan underside of the structural layer.
 20. A microscale switch forelectrostatic and electrothermal actuation, the switch comprising: (a) asubstrate; (b) a stationary electrode formed on the substrate; (c) astationary contact formed on the substrate; (d) a voltage source; (e) afirst current source; (f) a movable microcomponent suspended above thesubstrate, comprising: (i) a structural layer including at least one endfixed with respect to the substrate; (ii) a movable electrode positioneddirectly above the stationary electrode, spaced from the stationaryelectrode by a gap such that it does not contact the stationaryelectrode, and connected to the voltage source, the movable electrodebeing movable with respect to the stationary electrode when the voltagesource applies a voltage difference between the stationary electrode andthe movable electrode to establish electrostatic coupling between themovable electrode and the stationary electrode across the gap; (iii) amovable contact spaced from the stationary contact; and (iv) a firstelectrothermal component attached to the structural layer along amajority of a length of the structural layer and connected to the firstcurrent source, the first electrothermal component being operable toproduce heating when energized by the first current source forgenerating force for moving the structural layer; and (g) an electrodeinterconnect attached to a top surface of the structural layer oppositefrom the movable electrode and having electrical communication with themovable electrode.
 21. The switch of claim 20, wherein the movableelectrode and electrode interconnect have substantially equal respectivecoefficients of thermal expansion.
 22. A microscale switch forelectrostatic and electrothermal actuation, the switch comprising: (a) asubstrate; (b) a stationary electrode formed on the substrate; (c) astationary contact formed on the substrate; (d) a voltage source; (e) afirst current source; (f) a second current source; and (g) a movablemicrocomponent suspended above the substrate, comprising: (i) astructural layer including at least one end fixed with respect to thesubstrate; (ii) a movable electrode positioned directly above thestationary electrode, spaced from the stationary electrode by a gap suchthat it does not contact the stationary electrode, and onnected to thevoltage source, the movable electrode being movable with respect to thestationary electrode when the voltage source applies a voltagedifference between the stationary electrode and the movable electrode toestablish electrostatic coupling between the movable electrode and thestationary electrode across the gap; (iii) a movable contact spaced fromthe stationary contact; (iv) a first electrothermal component attachedto the structural layer along a majority of a length of the structurallayer and connected to the first current source, the firstelectrothermal component being, operable to produce heating whenenergized by the first current source for generating force for movingthe structural layer, wherein the first electrothermal component isattached to a top side of the structural layer for producing heat on thetop side of the structural layer to deflect the structural layer towardsthe substrate; and (v) a second electrothermal component attached to anunderside of the structural layer and connected to the second currentsource, the second electrothermal component being operable for producingheat on the underside of the structural layer when energized by thesecond current source for producing heat on the underside of thestructural layer to deflect the structural layer away from thesubstrate.